The use of fasteners, such as screws, bolts, and other threaded joining devices, continues to increase. However, the more a fastener is used, the more likely that its head becomes rounded off, worn, broken, or otherwise rendered useless. At that point, the fastener must be extracted from the workpiece and replaced.
Screw removing bits known in the art generally utilize a tool shaft capable of rotation, such as manual and power-driven screwdrivers and drills. As such, one end of the bit is inserted into a rotating shaft tool, while the other end of the bit is configured to impart rotational torque to a fastener held fast in a workpiece.
Several broken bolt extractors feature a left-handed cutting edge. For example, U.S. Pat. No. 4,777,850 discloses two such edges. However, such devices still require considerable power to impart the rotational torque necessary to “bite” into the fastener and begin left-handed extraction.
U.S. Pat. No. 6,595,730 B2 awarded to Bergamo on Jul. 22, 2003, discloses a bit for removing damaged screws. This device is designed to engage the exterior surface of a fastener rather than the interior surface. As such, “purchase” of the fastener by the device is relegated to the exterior surface.
Another example of a prior art extraction device is the tool disclosed in German patent DE 19526631 A1. The tool depicts two cutting edges that drill a hole in a “frozen” screw, bolt, or rivet when rotated in a first direction, afterwhich the two cutting edges are able to loosen the fastener thereby providing a single tool that performs two functions and reduces extraction time. With such a tool, however, a recess must be present in the fastener to better facilitate its removal from the workpiece. Accordingly, the German tool cannot be used to remove a fastener having a slotted surface configuration unless the fastener includes a recess with a depth sufficient to allow the two cutting edges to be inserted therein. Otherwise, the slotted head fastener would be damaged during removal.
A need exists in the art for a broken bolt/screw extraction device which facilitates the easy removal of a fastener held tight by a workpiece. The device should be capable of being used with manual, hand-actuated tools and/or electrically activated (including battery operated) tools. The device should engage as much of the interior surface of a fastener as possible to decrease the likelihood of a spin off of the device from the fastener while concurrently increasing the likelihood of extraction of the fastener with minimal force.